1. Field of the Invention
The invention relates generally to obstetric traction delivery devices, such as forceps and vacuum cups, and more particularly to a flexible, collapsible bonnet which is manually placed over the top of the fetus' head and unrolled, stopping short of the eyes and ears. When pulled, the bonnet utilizes graded and limited friction and internally-created vacuum forces to secure itself to the fetus' head, thus allowing orientation and application of traction forces to the fetus.
2. Description of Prior Art
Presently, forceps and vacuum cup devices are used for assisting child delivery in difficult cases. Typical instances occur when the parturient force of the mother is not sufficiently strong, or when there is a need to maneuver the fetus for delivery. Forceps may be padded and are typically made from unyielding materials, such as stainless steel. When such rigid material is engaged against the soft, moldable fetal head, undesirable and potentially damaging compression may occur. A faulty application or incorrect use of forceps may not only injure the fetus, but may cause maternal injuries as well. Since present day obstetrical training programs tend to vary in their emphasis on forceps use, those who use forceps likewise vary in forceps use proficiency. The less the proficiency, the greater the risk that either fetal or maternal injuries may follow.
While there have been numerous forceps modifications to suit specific indications, the basic forces acting on the fetal head are the same regardless of the particular type of forceps used. Compression of the fetal head between the two blades of the forceps provides the necessary force as traction is being applied by the obstetrician to effect delivery. Excessive compressive and/or traction forces may cause trauma to the fetus and possibly the mother.
Obstetric vacuum cups have also been utilized in order to apply an externally created vacuum force to the head of the fetus and thus adhere a traction device to the fetus' head. In the past these vacuum cups were made of metal, and to facilitate entry into the vagina the metal cup had to be formed in a size comparably smaller than the head of the fetus. Recent vacuum cups have been manufactured from firm rubbery substances, which because of their modest deformability may be manufactured in larger sizes and still fit in the vagina. Nevertheless, all vacuum cup devices utilized or described in the literature require that the material substance of the cup be firm enough to prevent collapse when an external vacuum source is applied.
Vacuum cups work on the following principle: When air inside the cup is mechanically evacuated through tubing connected to the cup body, a portion of the fetal head tends to be drawn into the cup, thus attaching the cup to the fetus and allowing application of traction force through the cup to the fetus. Once the cup is attached, the fetus is then pulled out of the uterus of the mother. In a conventional construction of an obstetric cup, there has been a tendency of the fetal head, still weak in structural strength, to be sucked into the cup. This may result in the rupture of small blood vessels in the fetus' scalp. In addition, damage to the surface of the fetal head is possible because of the firm grip between the hard vacuum cup and the soft fetal scalp. Maternal damage such as lacerations and hematomas in vacuum cup deliveries is also possible if part of the maternal interior gets caught between the vacuum cup and the fetal head.
A problem with vacuum cups is that a practitioner needs to apply a higher vacuum force if higher traction forces are needed. The higher vacuum force keeps the cup adhered to the fetus' head when the cup is subject to higher traction force. Typical commercial vacuum cups allow for as much as six hundred mm (Hg) of vacuum to be achieved within the cup by either a handheld or electric vacuum pump. Higher vacuum pressures tend to increase the possibility that the fetus will sustain injury to the head. In addition, if too little vacuum force is applied and the cup abruptly disengages, then damage may also result to the fetus' head. Thus presently a vacuum cup practitioner is left with concerns that too much vacuum may deform the fetus' head, and too little vacuum may allow the cup to abruptly disengage from the fetus' head.
Other devices for facilitating fetal delivery have also been cited in the literature. A noose-type device designed to be connected to the fetal neck was shown by U.S. Pat. No. 1,782,814. A soft hood-type barrel-shaped vacuum device designed to enclose the entire fetal head was described in U.S. Pat. No. 2,227,673. A vacuum cup with bowl-shaped recesses, tubular passages incorporated into the cup walls, and utilizing the application of an external vacuum source was described in U.S. Pat. No. 3,765,408. A non-vacuum traction net was shown in U.S. Pat. No. 4,597,391.
In summary, known prior art is limited to three basic discrete modes of attaching an obstetric device to the fetus: compressive forces, externally applied vacuum forces, or noose/net-type attachments that tie a traction apparatus to the fetus. Only forceps and vacuum cups are in commercial use at this time. In general, use of these devices has resulted in an incidence of significant maternal trauma of 10-15%, and an incidence of fetal trauma of 10-20%.
No obstetric traction device currently utilized in medical practice may be used without relatively high risk of trauma to the fetus, the mother, or both. For this reason, use of obstetric traction devices has been limited to those situations where the risks of not using the device outweigh the substantial risk of trauma to the fetus, mother, or both. As a result, many deliveries are unduly time-consuming and painful. Moreover, many deliveries which could be achieved vaginally are presently taken to Cesarean section, greatly increasing the risks to the mother to avoid unknown risks to the fetus.